Abstract
The combustion performance of 35% by mass dispersions of low, medium and high volatile coals in 950 Redwood second fuel oil have been investigated and compared with the combustion of the constituent fuel oil over a range of excess air from 2% to 30%. A low-pressure air-atomising Stordy-Hauck burner was used in a refractory lined flame tunnel, 3050 mm in length and 610 mm internal diameter. Each fuel was burnt at the rate of 22 litres per hour. Flame temperature, emissivity and length were measured. Particulate solids, NO[x] and SO[x] were determined in the flue gases. It was found that the flame length was increased by the presence of coal in the fuel oil. The flame with coal-oil dispersions is more thermally emissive than that of the constituent fuel oil alone. The emissions of SO[x] are reduced, NO[x] are increased and particulate emissions levels are higher from coal-oil dispersions, when compared to those from 950 Redwood second fuel oil alone. The calculated equilibrium NO and SO[3] concentrations in the flue gas compare favourably with those measured. Electron and optical micrographs of the particulate solids revealed different structures which suggest different combustion mechanisms. A combustion model is developed which successfully predicts flame lengths except in the case of the low volatile coal-oil dispersion.